A principal limitation of any sheet metal stamping process is the creation of an inhomogeneous deformation pattern (i.e., strain distribution pattern) across the sheet. Large, relatively flat regions of the panel may undergo little or no deformation, while areas with complex shapes and sharp features become heavily deformed and thereby work hardened. The amount of useful deformation that can be applied to the panel as a whole is thus limited by tearing failure (fracture) in those heavily worked regions, since they become incapable of withstanding any further deformation.
The stamping industry and academia have long struggled with this problem of inhomogeneous deformation patterns which limit the formability of a sheet. Many different approaches have been devised with the intention of minimizing the problem, since it cannot be totally eliminated. These include development of sheet metals with improved formability, use of lubricants which reduce friction between the sheet and the dies, improvements in die materials and finishes, improved die design methods, etc. All of these, however, have specifically focused on the problem areas themselves, viz. the heavily deformed localized regions which ultimately fail by tearing.